The present invention relates to vehicle suspension systems and more particularly computer controlled systems.
The traditional suspension systems used on motor vehicles are many and varied in concept but are currently all passive. They might look significantly different in construction but they all share two basic components, the spring and the damper, that have a major influence on their dynamic performance. Most systems for cars use steel springs in the form of a coil, a torsion bar, or a series of leaves although the use of air, rubber and plastic composites as springing media is increasing. The damper is invariably an hydraulic device. These components are asked to satisfy the conflicting performance requirements of ride comfort and vehicle handling over a wide range of operating conditions that include large payload changes, road types and profiles. In the case of the damper a single optimum setting cannot be provided to satisfy all these requirements. A low setting is required to provide good ride comfort unless the body mass has been excited at or near its resonant frequency when a high setting is required. The high setting is also required to control both the body and wheels during handling maneuvers. The conventional damper setting is thus a compromise and is gene rally set higher than is necessary for most conditions in order to deal adequately with the relatively infrequent exceptional events. A consequence of this compromise is that the damper sometimes generates significant and undesirable forces at the wrong time.
To provide a better overall performance therefore, a variable damper with at least two fixed settings has been proposed capable of operating at either setting. The benefits achievable using multi level dampers are highly dependent on the speed at which the setting can be changed, and the separation between settings.
As an alternative, gas suspension systems have been utilised either in pure pneumatic form or as a hydro-pneumatic system. These systems have the advantage that the vehicle can be maintained at any predetermined height which has the additional advantage that large spring deflections are always available. Also, the driver can alter the ride height at will which is particularly advantageous for bringing a platform level with e.g. a load dock or aiding access to the vehicle.
Recently hydraulic xe2x80x9cactive suspensionsxe2x80x9d have been developed. These were designed to eliminate the inevitable pitch and roll actions of a spring suspension by rapidly changing the lengths of rigid strut between each axle and the body of a vehicle. (An active suspension of this type might be imaged to lift each wheel over a bump and to push it down into a hole as required). The problem was that it is necessary for precisely-controlled physical movement to take place continually. It will be obvious that each movement takes time to complete, limiting its ability to deal with small disturbances at high speed. A certain amount of springing has to be retained to cope with this. The peak power demand problems and the complexity of the hydraulics also make the equipment expensive and impractical for high-volume use.
The present invention proposes a suspension system where the action of a pneumatic suspension unit is modified by an electromagnetic actuator, the modification being controlled by a software based controller in order to determine the modified characteristics.
The forces generated by the electromagnetic actuator are superimposed upon those of a pneumatic spring and are rapidly and precisely ) controlled in order to produce the desired effect. The electromagnetic actuator can combined with a pneumatic spring element as two separate items or as an integral assembly. The pressure in the pneumatic spring element may be continuously adjusted in accordance with the demands on the suspension.
The system is a very high speed force modulator, unlike any other type of actuator. Nothing has to move for it to control the forces transmitted to the vehicle by the wheels. It can respond in a fraction of a millisecond, so that wheel forces may be selectively isolated from or coupled to the vehicle, to any required degree, instant by instant for every inch of the vehicle motion, even at full speed. In effect, this turns a passenger car, a truck, an off-road vehicle or a military machine into a precisely-stabilised platform, moving under real-time electronic control. The electronically-controlled system is mechanically simple and inherently reliable. It is so designed that it can double as a gas spring that automatically adjusts to road conditions, temperature variations, vehicle load distribution and so on. Further, when driven iii reverse, it turns motion energy into electricity.
The system may be used in fully-active mode, drawing power directlyxe2x80x94from the vehicle to control the vertical forces at each wheel point, for the safest and smoothest ride possible. It can also operate in a semi-passive mode, taking power from the vertical motions of the wheels and using this to control the attitude and position of the vehicle, returning any surplus energy to a central source as electrical energy.
An advantage of using an electromagnetic actuator is that it has an armature the relative or change of position of which vis-a-vis its stator can be used to provide control signals which are supplied to the controller for one or more purposes such as control of the actuator to avoid limits of travel or to control the pneumatic spring pressure:
While reference is made to pneumatic springs and systems it is to be understood that any gas or mixture of gases can be used and not just air.
The suspension system is capable of operating in several different modes. It may be arranged to provide degraded on through a number of levels of performance